It is the long-term objective of this proposal to identify inbred mouse strains that express functionally distinct isoforms of the neuronal nicotinic receptor subunits alpha3, alpha4, alpha6, alpha7, and beta2. These subunits were chosen based on their potential roles in mediating the dependence-causing actions of nicotine. Identification of functionally distinct nicotinic receptor isoforms will be initiated by mutation analysis of the exons of the genes that encode these receptor subunits. Approximately forty inbred mouse strains of distinct genetic origins will be evaluated in the mutation screen. Once the mutation screen identifies nicotinic receptor subunit isoforms in mice with amnino acid differences, the appropriate cDNAs will be generated. Subsequently, the variant nicotinic receptor subunit isoforms will be evaluated in vitro for their pharmacological and functional properties. These experiments will lead to the establishment of a catalogue of mouse strains with known variations in nicotinic receptor subtype functional properties. This catalogue of mouse strains will serve as an important additional resource to evaluate the role of the various nicotinic receptor subunits in modulating the dependence-causing actions of nicotine. It has been estimated that 25 percent of all premature deaths in the United States are due to tobacco use. Despite the widespread knowledge of the health risks of smoking, approximately 25 percent of adults in the United States continue to smoke. Among smokers, nearly 80 percent say that they would like to quit although less than 5 percent successfully do so. It is well established that nicotine is the major dependence-causing agent in tobacco and that the initial actions of nicotine in the brain are mediated by nicotinic acetyicholine receptors. However, which nicotinic receptor subtypes mediate the dependence-causing actions of nicotine is poorly understood. To date, only modest success, at best, has been achieved in resolving this issue. The mouse strain nicotinic receptor "function" catalogue that will result from the studies outlined in this proposal will add a valuable resource for addressing this issue. By elucidating which nicotinic receptor subtypes are critical for the establishment of nicotine dependence, more effective pharmacological strategies for smoking cessation may be developed.